Buy ya RAM in matched pairs. It definitely does NOT need to be 1.5 ..... most so called 1.5v RAM runs at 1.65 v under the advertised DDR3 speed which requires engaging the XMP profile or setting the speed , voltage and timings manually.
Sandy Bridge does not demand only 1.5v modules, it will be perfectly happy with 1.65v modules too. If someone tries to tell you that you must have 1.5v modules, then they are either trying to sell them to you, or they have been reading misinformation, or both! Another point to consider here, is that in your BIOS, if you head to the memory voltage setting, and enter 1.5v, the text will remain white/grey, if you enter 1.65v, it will turn yellow, and it isn't until 1.73v that it turns red, so at the moment, I'd rest assured that 1.65v modules are OK to use, and I have had this confirmed by Asus, Gigabyte and Corsair so far, as soon as I hear from anyone else, I will update this again.
I can't see buying a "crappy case" and then redoing hours of work later to do it over again.